1. Field of the Invention
This invention relates to a solderless terminal which is adapted to be electrically connected to an insulated lead wire without removal of the insulating cover, and more particular to an improvement of the solderless terminal which results in miniaturization and increased mechanical strength.
2. Background
A variety of solderless terminals have been proposed in the art because they can be readily connected to lead wires. A number of such solderless terminals are shown in FIGS. 15 through 21.
The solderless terminal shown in FIGS. 15 and 16 has been disclosed in Japanese (unexamined) Utility Patent Application No. 142463/1985. The solderless terminal 1 comprises a front end portion including an electrical contact portion 2 which is engaged with a mating connecting terminal; a rear end portion including a lead-wire fixing portion 7 having right and left crimping pieces 5 and 6 which are designed to be crimped around the insulating cover 3 of a lead wire 4; a conductor connecting portion 9 provided between the electrical contact portion 2 and the lead wire fixing portion 7 which is electrically connected to the conductor 8 of the insulated lead wire 4 (hereinafter referred to as "a core-wire 8", when applicable); a first constricted portion 10 provided between the electrical contact portion 2 and the conductor connecting portion 9; and a second constricted portion 11 provided between the conductor connecting portion 9 and the lead-wire fixing portion 7. The terminal including the above parts is a single piece stamped out of a sheet of conductive metal plate.
The conductor connecting portion 9 includes front and rear plate-shaped contact pieces 14 each having a core-wire contact slot 13 which are spaced from each other in the direction along the longitudinal axis of the terminal 1. The plate-shaped contact pieces 14 are formed by raising portions of the bottom 15 of the press-contact terminal 1. Each of the plate-shaped contact pieces 14 include right and left clamping blades 17 which define the core-wire contact slot 13 between them. The clamping blades 17 function to cut the insulating cover 3 of the insulated lead wire 4 and retain the core-wire 8, so that the solderless terminal 1 is electrically connected to the conductor 8 of the insulated lead wire 4 which is fixedly held by the lead-wire fixing portion 7 of the terminal 1.
FIGS. 17 and 18 show another conventional solderless terminal, which has been disclosed in U.S. Pat. No. 4,385,794. The solderless terminal 20 is fundamentally the same as the one shown in FIG. 15. That is, the solderless terminal 20 is also formed as one piece by stamping out a piece of conductive metal plate, and it comprises: a front end portion including an electrical contact portion 2 which is adapted to be engaged with a mating connecting terminal; a rear end portion including a lead wire fixing portion 7 having right and left crimping pieces 5 and 6 which are designed to be crimped around the insulated cover 3 of the lead wire; a conductor connecting portion 9 provided between the electrical contact portion 2 and the lead wire fixing portion 7 which is electrically connected to the conductor of the insulated lead wire; a first constricted portion 10 between the electrical contact portion 2 and the conductor connecting portion 9; and a second constricted portion 11 between the conductor connecting portion 9 and the lead-wire fixing portion 7. The conductor connecting portion 9 includes conductor clamping blades 17 confronting with each other to define core-wire contact slots 13 which are spaced from each other in the direction of the longitudinal axis of the terminal.
However, it should be noted that, in the solderless terminal 20, the first and second constricted portions 10 and 11 are merely flat plates which are provided by using the bottom plate of the terminal. The conductor connecting portion 9, as shown in FIG. 18, includes right and left side walls 22 and 22 which are formed by bending both sides of the bottom plate 21. The front and rear end portions of those side walls 22 and 22 are bent inwardly so that they function as the aforementioned conductor clamping blades 17. The right and left side walls 22 and 22 define a lead-wire accommodating space 23 for accommodating the end portion of a lead-wire to be press-connected to the terminal. Cuts 24 are formed in the ridges of the conductor connecting portion 9 where the bottom plate 21 meets the right and left side walls 22, to increase the mechanical strength thereof.
Other conventional solderless terminals, shown in FIGS. 19 and 20, and in FIG. 21, have been disclosed in Japanese (unexamined) Utility Patent Application No. 35266/1988. The solderless terminal 26 shown in FIGS. 19 and 20 is obtained by improving the pressure-connect type terminal 20 shown in FIG. 17. That is, the right and left side walls 22 and 22 of the conductor connecting portion 9 have cut-outs which allows the insulating cover 3 of the insulated lead wire 4 to expand when the latter is compressed. Similarly as in the case of the solderless terminal 20 shown in FIG. 17, the front and rear end portions of the side walls 22 are bent inwardly, to form conductor clamping blades 17.
The solderless terminal 27 shown in FIG. 21 represents a slight modification of the solderless terminal 26 shown in FIG. 19. That is, in order to increase the mechanical strength of the side walls 22 of the conductor connecting portion 9, the cut-outs 28 are modified into rectangular windows leaving the outer edge portions of the side walls.
The above-described solderless terminals are generally produced on a large scale. Therefore, even if the degree of miniaturization and amount of reduction in weight of each of the solderless terminals are small, the miniaturization and the weight reduction greatly contribute to the economical use of the material. On the other hand, the solderless terminals are, in general, used as follows: A number of solderless terminals are arranged in side-by-side relationship within a connector. Therefore, even if the degree of miniaturization per solderless terminal is small, the connector can be greatly miniaturized.
Thus, in the connector art, intensive research has been conducted in miniaturizing solderless terminals, and in reducing the thickness of the metal plates to be used for fabricating such terminals.
In the solderless terminal 1 shown in FIGS. 15 and 16, in order to prevent the conductor clamping blades 17 from being deflected outwardly by the pressure applied thereto when the conductor 8 of the lead wire is pushed into the core-wire contact slots 13, the conductor clamping blades 17 defining the core-wire contact slots 13 are formed by upwardly bending the portions of the bottom plate 15 between the right and left side walls 29 and 29 of the conductor connecting portion 9. Hence, in order to miniaturize the solderless terminal, it is essential to reduce the width h of each of the conductor clamping blades 17. However, the reduction of the width h is considerably difficult, because, in a blanking process and in a bending process using a jig to form the solderless terminal, the processing accuracy is limited, and accordingly dimensions to be handled are limited. Thus, miniaturization of the solderless terminal 21 shown in FIGS. 15 and 16 is not practical.
As was described above, the solderless terminals 20, 26 and 27 shown in FIGS. 17 through 21 include the constricted portions 10 and 11. These portions 10 and 11 are simple flat plates, which are parts of the bottom plate, and therefore lower in mechanical strength than the other portions. Hence, if the weight of the solderless terminal is reduced by decreasing the thickness of the plate material used, then the constricted portions 10 and 11 may be deformed or damaged when the terminals thus formed are inserted into the connector housing.
In the solderless terminals 26 and 27 shown in FIGS. 19 and 20, and 21, the side walls 22 have the cut-outs 28 formed therein. The formation of the cut-outs 28 lowers the joining strength between the side walls 22 and the bottom plate. Hence, when the conductor of the lead wire is inserted into the core-wire contact slots 23, the pressure applied to the conductor clamping blades 17 tends to concentrate on the junctions (bent parts) between the bottom plate and the front and rear end portions of the side walls 22. Therefore, if the plate material to be used for fabricating of the terminal is reduced in thickness, the mechanical strength will be attendantly decreased as described above. As a result, when the conductor of the lead wire is pushed into the core-wire contact slots, the conductor clamping blades 17 will be urged outwardly from each other, thus adversely affecting the press-connection of the terminal to the conductor of the lead wire.
Accordingly, an object of the invention is to eliminate the above-described difficulties accompanying conventional solderless terminals. More specifically, an object of the invention is to provide a solderless terminal in which its portions which are heretofore low in mechanical strength, such as the first constricted portion between the electrical contact portion, the conductor connecting portion and the second constricted portion between the conductor connecting portion and the lead-wire fixing portion, are increased in mechanical strength, whereby, even when the terminal is reduced in size and in weight by decreasing the thickness of a plate material to be used for fabrication of the terminal, the terminal remains mechanically strong. Therefore, the terminal will remain electrically connected to the conductor of the insulated lead wire with high reliability at all times.